EFFECTS OF HUMAN RECREATION ON THE INCUBATION BEHAVIOR OF AMERICAN OYSTERCATCHERS

2006·6.8 MB·English

by  Conor P Mcgowan

The Wilson Journal ofOrnithology 118(4):485-493, 2006
EFFECTS OF HUMAN RECREATION ON THE INCUBATION
BEHAVIOR OF AMERICAN OYSTERCATCHERS
CONOR P. McGOWAN1’3’4 AND THEODORE R. SIMONS2
—
ABSTRACT. Human recreational disturbance and its effects on wildlife demographics and behavior is an
increasingly important area of research. We monitored the nesting success of American Oystercatchers (Hae-
matopus palliatus) in coastal North Carolina in 2002 and 2003. We also used video monitoring at nests to
measure the response of incubating birds to human recreation. We counted the number oftrips per hour made
by adult birds to and from the nest, and we calculated the percent time that adults spent incubating. We asked
whether human recreational activities (truck, all-terrain vehicle [ATV], and pedestrian traffic) were correlated
with parental behavioral patterns. Eleven apriori models ofnest survival and behavioral covariates were eval-
uated using Akaike’s Information Criterion (AIC) to see whether incubation behavior influenced nest survival.
Factors associated with birds leaving their nests (n = 548) included ATV traffic (25%), truck traffic (17%),
pedestrian traffic (4%), aggression with neighboring oystercatchers orpaired birds exchanging incubation duties
(26%), airplane traffic (1%) and unknown factors (29%). ATV traffic was positively associated with the rate of
trips to and away from the nest (p, = 0.749, P < 0.001) and negatively correlated with percent time spent
incubating (3, = -0.037, P = 0.025). Otherforms ofhuman recreation apparently had littleeffectonincubation
behaviors. Nest survival models incorporating the frequency of trips by adults to and from the nest, and the
percentage oftime adults spent incubating, were somewhat supported in the AIC analyses. A low frequency of
trips to and from the nest and, counter to expectations, low percent time spent incubating were associated with
higherdaily nest survival rates. These datasuggestthatchanges in incubation behaviormightbeonemechanism
by which human recreation affects the reproductive successofAmerican Oystercatchers. Received28July2005,
accepted24 April 2006.
The effect ofhuman recreational activity on tercatcher (Haematopuspalliatus) populations
wildlife is an increasingly important area of in the Mid-Atlantic states are declining (Ma-
research (Burger 1981, Burger and Gochfeld whinney and Bennedict 1999, Davis et al.
1998, Fitzpatrick and Bouchez 1998, Whitta- 2001). The U.S. Shorebird Conservation Plan
ker and Knight 1998, Carney and Sydeman lists the American Oystercatcher as a “Spe-
1999). Human disturbance has been linked to cies of High Concern,” due, in part, to human
altered foraging behavior (Burger 1981, Bur- encroachment on breeding habitat (Brown et
ger and Gochfeld 1998, Fitzpatrick and al. 2001). Evidence that humans are directly
Bouchez 1998, Rodgers and Schwikert 2003, responsible for American Oystercatcher nest
Stolen 2003) and diminished reproductive failure is limited (Davis et al. 2001, McGowan
success of many waterbird species (Hunt 2004); however, human recreation is often as-
1972, Robert and Ralph 1975, Tremblay and sociated with lower oystercatcher reproduc-
Ellison 1979, Safina and Burger 1983, Rhulen tive success (Hockey 1987, Jeffery 1987,
et al. 2003). The mechanisms by whichhuman Novick 1996, Davis 1999, Leseberg et al.
disturbance lowers reproductive success, how- 2000, Verhulst et al. 2001, McGowan 2004).
ever, are poorly understood. Because American Oystercatcher populations
Current data indicate that American Oys- may require intensive management in the near
future, it is important to understand the rela-
1 North Carolina Coop. Fish and Wildlife Research tionship between human recreation and oys-
CUnaimt,puDsepBto,xof76Z1o7o,loRgalye,igNho,rtNhCC2a7r6ol9i5n,aUSStAat.e Univ., tercatcher nesting success (Brown et al. 2001,
2U.S. Geological Survey, North Carolina Coop. Davis et al. 2001).
Fish and Wildlife Research Unit, Dept, of Zoology, Skutch (1949) hypothesized that higher lev-
North Carolina State Univ., Campus Box 7617, Ra- els of parental activity during the nesting pe-
leigh, NC 27695, USA. riod might lead to greater rates of predation
3Current address: Dept, of Fisheries and Wildlife, because more activity makes nests more ob-
302 Anheuser Busch Natural Resources Bldg., Univ.
ofMissouri, Columbia, MO 65211, USA. vious to predators. Because American Oyster-
4Corresponding author; e-mail: catchers are ground-nesting shorebirds that are
[email protected] easily flushed from their nests (Davis 1999),
485
n
486 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 4, December2006
we similarly hypothesized that human recre- use the beaches for walking, shell collecting,
ation might increase the activity ofincubating swimming, and fishing, and they drive four-
oystercatchers, thereby leading to increased wheel drive passenger vehicles (ORVs) and
predation rates. Although Skutch’s hypothesis smaller, all-terrain vehicles (ATVs) on the
has been tested extensively, conclusions are beach. Vehicles are permitted along a network
mixed (Martin 1992, Roper and Goldstein of unpaved roads behind the primary dunes
1987, Martin et al. 2000, Tewksbury et al. and anywhere on the open beach, except in
2002). We believe that nesting American Oys- designated areas that are closed to protect veg-
tercatchers provide a good opportunity to test etation, nesting sea turtles, and shorebirds, and
Skutch’s hypothesis because their nests are to prevent erosion.
—
relatively easy to find and monitor, and they Data collection. We located oystercatcher
—
experience high rates of nest predation (Nol nests (n 268) and, from 15 April until 30
and Humphrey 1994. Davis et al. 2001, Sa- July in 2002 and 2003, checked their status
bine et al. 2005). every 3-4 days until chicks hatched or the
In this study, we used video monitoring to nests failed. We used SONY HI-8 video cam-
record human recreational activity and the be- eras to record the incubation behavior ofnest-
havior of incubating oystercatchers nesting on ing adults at randomly selected nests ( = 72).
the Outer Banks of North Carolina. We asked We videotaped nests on Bodie Island and Hat-
whether human recreational activity altered teras Island (Cape Hatteras National Sea-
the behavior of nesting birds, and whether in- shore), and on North Core Banks and South
creased parental activity or decreased nest at- Core Banks (Cape Lookout National Sea-
tendance were associated with higher rates of shore). Nests were filmed for approximately
nest failure. 4-hr intervals at least once between the com-
pletion of egg laying and hatching. In the ab-
METHODS
sence of human recreational activity, we as-
—
Study areas. We monitored nesting suc- sumed that parental behavior would be natural
cess of American Oystercatchers at Cape and homogenous throughout the incubation
Lookout (76° 32' W, 34° 36' N) and Cape Hat- period. Evidence indicates that both American
teras (75° 31' W, 35° 24' N) national seashores and Black (Haematopus bachmani) oyster-
in North Carolina during 2002 and 2003. The catchers incubate their eggs 90-100% of the
seashores comprise >160 km ofbarrier island time once the clutch is completed, and that the
habitat that supports —90 breeding pairs of amount oftime spent incubating does not vary
American Oystercatchers. All work at Cape during the incubation period (Nol and Hum-
Lookout National Seashore was conducted on phrey 1994, Andres and Falxa 1995). Verbo-
North Core Banks and South Core Banks (see ven et al. (2001) showed that Eurasian Oys-
Godfrey and Godfrey 1976 for site descrip- tercatchers incubated 85-90% of the time at
tion). Cape Hatteras National Seashore com- undisturbed nests, and that the percentage of
prises three main islands: Bodie, Hatteras. and time spent incubating was constant between
Ocracoke Islands. These barrier islands are the end of the laying period and hatching.
long, narrow, and bordered by sandy beaches Studies of other shorebird species indicate
on the ocean side and salt marshes on the similar incubation patterns (Norton 1972), al-
sound side. American Oystercatchers nest on though Cartar and Montgomerie (1987) found
the ocean side beaches, dunes, and adjacent that nest attendance of White-rumped Sand-
sand flats. Raccoons (Procyon lotor) and feral pipers (Calidris fuscicollis) may vary daily,
cats (Felis catus) are common on all islands depending on weather or other environmental
except Ocracoke, which has no raccoons. The factors.
islands are open to the public and most beach- Novick (1996) reported that human activity
es are open to vehicles. Approximately on South Core Banks at Cape Lookout Na-
650,000 people visit Cape Lookout each year: tional Seashore was distributed “fairly even-
the visitation rate at Cape Hatteras is consid- ly” throughout the day and was greater on
erably higher and has increased steadily from weekends (Friday-Sunday) than on weekdays.
1.5 million in 1986 to 2.2 million in 2005 Novick (1996) also reported that humans con-
(National Park Service 2005). Park visitors centrated around activity centers, such as the
McGowan and Simons • HUMAN RECREATION ALTERS INCUBATION BEHAVIOR 487
ferry dock, the lighthouse, and the ocean in- which one of the above causal factors fol-
lets at the north and south ends ofSouth Core lowed. We also report the percent ofobserved
Banks. Our nests were filmed between 07:00 human recreational activities that were pre-
and 14:00 EST, on both weekdays and week- ceded by a bird leaving its nest.
ends, which we believe provided an unbiased We used linear regression models (Neter et
representation of human disturbance and pa- al. 1996) to determine whether human recre-
rental activity patterns at each nest. ational factors were correlated with oyster-
Each video camera was housed in a weath- catcher parental activity. Trips per hr and per-
erproof plastic container attached to a metal cent time spent incubating were modeled as
stand, and placed approximately 5 m from the dependant variables, with number of ORVs,
nest to avoid disturbing incubating birds. ATVs, and pedestrians passing a nest per hr
Most cameras faced the ocean and recorded serving as the independent variables.
activity both in the vicinity ofthe nest and on For camera-monitored nests, we used the
open beach beyond the nest. Sometimes cam- logistic exposure method to estimate daily
eras were placed at nests located in the dunes nest survival (Shaffer 2004). We used SAS
or other locations where the ocean-side beach (ver. 9.1; SAS Institute, Inc. 2003) to generate
was not visible. In these cases, we directed survival estimates and to test competing mod-
cameras toward the most likely source of hu- els of nest survival with parental behaviors as
man recreation (e.g., the dune road at Cape covariates (Shaffer and Thompson in press).
Lookout). The area sampled by the video We tested 1 1 a priori models (Table 1) that
camera was different for each nest due to dif- modeled trip rate and percent time incubating
ferences in the surrounding landscape; there- as both continuous and categorical variables.
fore, detection probabilities for human activ- We used two methods for categorizing the
ities were heterogeneous among nests. We re- data: one purely statistical and one based on
viewed tapes in real time to count the number behavioral observations. For statistical cate-
of trips by incubating birds to and from the gorical models, we split the data for number
nest per hr, and the percent time that adults of trips/hr (Tripcat) and percent time incubat-
spent incubating. Herein, the term “trip” re- ing (Inccat) into low and high categories, us-
fers to a bird leaving or returning to its nest. ing the median value of each as the cut-off
We also counted the number of ORVs, ATVs, point (Tripcatl: <3.69 trips/hr = low, >3.69
and/or pedestrians pas—sing each nest per hr. trips/hr = high; Inccat1: <85% = low, >85%
Statistical analyses. We used the Mayfield = high). For the second method (biological
(1961, 1975) method to estimate daily nest categorical models), we used the average val-
survival rates and hatching success for all ues from seven nests that had no evidence of
nests monitored. We applied the Mayfield es- human disturbance; we then divided the data
timate to entire clutches and did not consider into a new set of low and high categories. In
individual egg survival. Heterogeneity in sur- this case, undisturbed nests averaged 2.25
vival probabilities during the incubation stage trips per hr. Therefore, we used three trips per
was not considered, and the midpoint rule was hr as a conservative estimate of oystercatcher
used to designate the time of failure and time nest site activity in the absence ofhuman dis-
ofhatching for nests that failed or hatched be- turbance (Tripcat2: <3.0 trips/hr = low, >3.0
tween visits. We considered nests successful trips/hr = high). Time spent incubating by un-
if at least one egg hatched, and failed when disturbed birds averaged 90% of the obser-
all eggs were lost. Partial nest failure was not vation period; thus, we used 90% as the cut-
considered in this study. off point to categorize nests as low or high in
Each time a bird left its nest we estimated terms of percent time spent incubating (Inc-
the time between departure and the time at cat2: <90% = low, >90% = high). We mod-
which the probable causal event occurred. eled each categorical variable separately and
Possible causal factors included: ATV, ORV, in a model that included both trip rate and
pedestrian, and airplane traffic, as well as in- percent time incubating (Table 1). One model
teractions between territorial pairs and ex- included a year effect, and we tested a null
changes in incubation duties. We report these model (null) that assumed constant survival
data as the percent of nest departures for over the season. We used an information the-
n n n n
488 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 4, December2006
TABLE 1. Eleven candidate models used to examine the relationship between daily nest survival and pa-
rental incubation behaviors ofAmerican Oystercatchers nesting on the Outer Banks of North Carolina in 2002
and 2003.
Candidatemodel Modelcovariates
Global Continuous Year, trips to and from the nest per hr, percent incubation time
Year Year
Models with statistically categorized data (splitting low and high data at the median value)
Global categorization 1 Year, tripcatl, inccatl3
Tripcatl + inccatl Tripcatl, inccatl
Tripcat1 Tripcat1
Inccatl Inccatl
Models with biologically categorized data (splitting data at the average value for undisturbed nests)
Global categorization 2 Year, tripcat2, inccat2
Tripcat2 + inccat2 Tripcat2, inccat2
Tripcat2 Tripcat2
Inccat2 Inccat2
Null No covariates, assumes constant survival
aInccatl,inccat2,tripcatl,andtripcat2arecategoricalvariablesintowhichnestswerecategorizedasloworhighintermsofpercenttimeadultbirds
spentincubating(inccat)orthenumberoftripsadultsmadetoandfromthenest/hr(tripcat),accordingtothecriteriathatfollow:inccatl:<85%=low,
>85% = high;inccat2: <90% = low,>90% = high;tripcatl: <3.69trips/hr= low,>3.69trips/hr=high;tripcat2: ^3.0trips/hr= low,>3.0trips/hr
= high.
oretic approach to rank the models from most to weather, human destruction, or abandon-
to least supported, base—d on Akaike’s Infor- ment ( = 6).
mation Criterion (AIC) using AIC AAIC Though not true experimental controls,
c, c,
and Akaike weights (w,); Burnham and An- there were seven nests at which we observed
derson 2002). Means are reported ±SE. no human disturbance during filming. Birds at
those nests incubated for 90% ± 0.033 ofthe
RESULTS filming period and made 2.25 ± 0.60 trips/hr
We monitored 185 nests at Cape Lookout compared to 82% ± 0.017 incubation and
and 83 nests at Cape Hatteras. The overall 3.66 ± 0.17 trips/hr at all other nests. The
Mayfield estimate of daily nest survival was number of trips/hr at undisturbed nests was
0.92 ± 0.006 at Cape Lookout and 0.94 ± significantly lower (t — 2.27, P = 0.026) than
0.007 at Cape Hatteras. The highest daily nest at all other nests. The percent of time spent
survival rates were recorded at Cape Hatteras incubating at undisturbed nests was not sig-
in 2003 (0.96 ± 0.008), and the lowest were nificantly greater (t = 1.34, P = 0.19) than it
recorded at Cape Lookout in 2002 (0.90 ± was at disturbed nests.
0.007); these were the only year and location We recorded 539 instances in which incu-
comparisons that were significantly different bating birds departed their nests. Of those in-
(Z = 4.83, P < 0.001). stances, ATVs were filmed within 3 min of
We filmed 72 nests for a total of 320.18 hr nest departure on 136 occasions (25%) and
and a mean of 4.45 ± 1.19 hr per nest. Most ORVs were filmed 92 times (17%) within 3
nests were filmed once for ~4 hr, but some min of departure. We recorded a total of 284
were filmed twice before they hatched or ATVs, 62% ( = 177) of which passed by a
failed. We excluded one nest from the analysis nest within <3 min of a bird departing its
where it appeared that the bird’s behavior was nest. We observed 1,466 ORVs pass by filmed
affected by the presence of the video camera. nests, but only 11% (n = 168) passed by with-
Of the 72 nests filmed, chicks successfully in 3 min of a bird leaving its nest. Groups or
hatched from 19 and 53 nests failed. Sixty two individual pedestrians were filmed 19 times
percent of nest failures were due to mamma- (4%) within 10 min of nest departures. Of all
lian predation (n — 32), 28.5% failed for un- the 110 pedestrians that we observed, 33% (
known reasons ( = 15), and 11% were lost = 36) passed by within 10 min of a bird de-
n
McGowan and Simons • HUMAN RECREATION ALTERS INCUBATION BEHAVIOR 489
parting its nest. Eight percent ( = 44) ofnest
departures were associated with territorial dis-
putes and 18% (n = 108) with the exchange
in incubation duties. Eight departures (1%)
were associated with low-flying airplanes that
passed within 3 min of nest departure. For the
remaining 29% (n = 154) of nest departures,
no disturbances, territorial interactions, or in-
cubation exchanges took place following de-
parture.
Regression models showed that there was
little or no association between ORV traffic
and the rate at which incubating oystercatch-
ers made trips to and from their nests ((3, =
0.018, P = 0.064) or the percent time they
spent incubating — 0.0006, P = 0.57).
(f3t
Likewise, pedestrian traffic was not associated
with a significant reduction in the percent time
incubating ((3 = -0.005, P = 0.75) or birds
t
making more trips to and from their nests per
hr = -0.268, P = 0.079). Increased ATV
((3!
traffic, however, was associated with a reduc-
FIG. 1. The effect of all-terrain vehicle (ATV) tion in the percent time spent incubating ((3!
beach traffic onincubationbehaviorofAmericanOys- = —0.037, P = 0.025) and an increase in the
tsiehnrigcpattbhceehte2wr0es0e2onnatnthhdeep2Oe0ur0tc3eenrbtrBeoaefndktiisnmgeofsseNpaoesnrotntshi:nCc(auArb)oaltriienlnaagtdiauonrnd-- rPat<e o0f.0t0ri1p;sFtiog.an1d).from the nest ((3! = 0.749,
the average number of ATVs passing per hour (P, = All models except the global continuous
-0.037, P = 0.025), and (B) relationship between the model received some level of support, but no
number of trips to and from the nest per hr and the model had overwhelming support (Table 2).
number of ATVs passing per hr (P, = 0.749, P < The tripcat2 model (i.e., nests divided into
0001
. ). low and high categories based on average trip
rate for nests with no observed human distur-
TABLE 2. Candidate models examining the relationshipbetween daily nest survival and parental incubation
behaviors ofAmerican Oystercatchers nesting on the Outer Banks ofNorth Carolina in 2002 and 2003. Models
are ranked in descending order of support based on Akaike’s information criteria AICc, AAICc, and Akaike
weights (w,).
Model Log-likelihood No.parameters AICc AAICc W/
Tripcat2a -159.62 2 323.27 0.00 0.28
Null -161.08 1 324.16 0.89 0.18
Tripcat2 -1- inccat2a -159.62 3 325.29 2.02 0.10
Inccatl -160.68 2 325.39 2.11 0.097
Inccat2 -160.77 2 325.56 2.29 0.089
Tripcat1 -160.98 2 325.99 2.72 0.072
Year -161.07 2 326.17 2.90 0.066
Tripcatl + inccatl -160.26 3 326.56 3.29 0.054
Global categorical2 -159.56 4 327.18 3.92 0.040
Global categorical1 -160.24 4 328.54 5.28 0.020
Global continuous -261.36 4 530.79 207.52 0.000
aInccatl,inccat2,tripcatl,andtripcat2arecategoricalvariablesintowhichnestswerecategorizedasloworhighintermsofpercenttimeadultbirds
spentincubating(inccat)orthenumberoftripsadultsmadetoandfromthenest/hr(tripcat),accordingtothecriteriathatfollow:inccatl:<85%=low,
>85% = high;inccat2: <90% = low,>90% = high;tripcatl: <3.69trips/hr= low,>3.69trips/hr=high;tripcat2: <3.0trips/hr=low,>3.0trips/hr
= high.
490 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 4, December2006
TABLE 3. Daily survival estimates and hatching probability estimates for nests in two categories ofbehav-
ioral data collected from American Oystercatchers nesting on the Outer Banks of North Carolina in 2002 and
2003.
Dailyprobability Lower/upper Hatching
Category No.nests ofsurvival confidenceintervals probability
Median cutoffs
<3.69 trips/hr 37 0.958 0.935 / 0.973 0.314
>3.69 trips/hr 35 0.948 0.925 / 0.965 0.240
Incubation <85% 32 0.961 0.938 / 0.975 0.338
Incubation >85% 40 0.945 0.922 / 0.962 0.218
Zero-observed-disturbance average cutoffs
<3.00 trips/hr 26 0.969 0.946 / 0.982 0.424
>3.00 trips/hr 46 0.944 0.924 / 0.960 0.213
Incubation <90% 50 0.967 0.945 / 0.980 0.400
Incubation >90% 22 0.948 0.926 / 0.964 0.237
bance as the only covariate) had the highest American Oystercatchers. ATV traffic was as-
rank of all the models (AAICc = 0.00, w, = sociated with increased rates of trips to and
0.28). The null model was ranked second from the nest and reduced time incubating;
(AAIC = 0.89, w, = 0.18), and the model other forms of human recreation were more
c
incorporating both tripcat2 and inccat2 was weakly associated with oystercatcher nesting
ranked third (AAIC = 2.02, w, = 0.10). All behaviors. Sixty two percent ofthe ATVs that
c
the models with categorical behavioral vari- we observed passed within 3 min of a bird
ables, the year model, and the null model had departing its nest, whereas the same was true
a AAICc of <7 and weights between 0.02 and for only 1 1% of the ORVs that we observed.
0.28 (Table 2). Generally, models with a Birds appear to have habituated to the pres-
AAIC of <7 cannot be ruled out, but models ence of ORVs (Whittaker and Knight 1998),
c
with weights <0.70 cannot be exclusively ac- but they view ATVs (and to a lesser extent,
cepted (Burnham and Anderson 2002). pedestrians) as threats. Peters and Otis (2005)
The estimated daily survival rate for nests reported that wintering American Oyster-
with <3.69 trips to and from the nest per hr catchers habituated to boat traffic on the in-
was greater than the daily survival rate for tercoastal waterway in South Carolina. Other
nests with >3.69 trips to and from the nest studies have shown that birds respond differ-
per hr (Table 3). That same pattern was ob- ently to different forms of human recreational
served when the data were divided into cate- disturbance (Burger 1981), but most have fo-
gories representing nests with ^3 trips per hr cused only on changes in foraging behavior
and >3 trips perhr. Nests in which the parents (Burger and Gochfeld 1998. Rodgers and
incubated for <85% ofthe observation period Schwikert 2003, Stolen 2003). Our study is
had higher daily survival probabilities than one of the few to investigate how human rec-
nests in which incubation percentages were reational disturbance affects incubation be-
>85%. The same pattern was observed when havior. ATVs are louder and move faster than
we categorized the data by nests in which ORVs and pedestrians, which might explain
adults spent <90% and >90% time incubat- why the birds are affected more by ATV traf-
ing. These data indicated that nests in which fic (Burger 1981, Burger and Gochfeld 1998).
parents made more trips to and from the nest ORVs and pedestrians also tend to stay closer
had a lower daily survival probability, and to the firm sand along the water’s edge, which
that nests where the parents spent more than means they generally travel farther from nest-
85-90% of their time incubating had a lower
ing birds.
chance of surviving each day.
Although the probability of hatching was
DISCUSSION low in all nests, regardless ofparental activity,
Our data show clear associations between we did find evidence that human recreational
human recreation and incubation behavior of disturbance may reduce the nesting success of
McGowan and Simons • HUMAN RECREATION ALTERS INCUBATION BEHAVIOR 491
American Oystercatchers by altering incuba- mately 1 hr at mid day hatched successfully.
tion behavior. Analyses based on AIC model One videotaped nest hatched successfully,
selection indicated that the rate of parental even though the parents incubated for only
trips to and from the nest and the percent time 66.8% of the 4.07-hr observation period. Egg
that parents spent incubating may have af- hardiness may reflect an adaptation that en-
fected daily nest survival rates. Although no ables parents to reduce nest-site activity. Par-
model received overwhelming support, none ents that depart their nest and wait until mul-
of the categorical behavioral models could be tiple disturbances have passed before return-
ruled out. The daily survival estimates indi- ing may have greater nesting success than par-
cated that nesting adults that made fewer trips ents that return to their nests quickly and flush
to and from the nest had greater daily nest repeatedly. Future analyses should assess the
survival rates. Conversely, nests where the effect that the average amount of time birds
parents incubated for less time had higherdai- spend off the nest has on nest success.
ly survival rates. We hypothesize that mam- There were several potential sources of
malian nest predators, the primary nest pred- measurement error in our study that might ex-
ators in this system (Davis et al. 2001), are plain why no models were strongly supported.
better able to find disturbed nests through Incubation behavior might vary as birds ha-
smell because each time a parent gets up and bituate to disturbance (Whittacker and Knight
walks away from a nest it leaves a scent trail 1998). Because the field of view varied at
that raccoons and cats may follow. Ourresults each nest, our cameras recorded areas of dif-
differ from those of Verboven et al. (2001), ferent size for each nest, and we were unable
but that is likely because the primary nest to control forthese differences in the analyses.
predators in that system were avian predators. We were also unable to measure the distance
ATV traffic is not the only factor affecting from the nests to the disturbance recorded on
oystercatcher nesting success on North Caro- our video. Several studies have shown that the
lina’s Outer Banks. Nest predation is an im- proximity of human disturbance has a major
portant determinant ofhatching success in the effect on the behavioral responses of birds
Outer Banks (Davis et al. 2001, McGowan et (Burger and Gochfeld 1998, Rodgers and
al. 2005), and relationships between human Schwikert 2003). It is likely that in some cas-
recreation and nest predators are poorly un- es, recreational activity recorded by our cam-
derstood. Vehiculartraffic also may affectsuc- eras did not elicit a response from the incu-
cess during the chick-rearing phase of repro- bating bird because the activity was too far
duction. In the 2003 breeding season, we con- away. Video monitoring is an extremely use-
firmed that five chicks from three different ful tool for studying avian behavior; however,
nests were run over by vehicles on the beach- future studies ofhuman disturbance using vid-
es of South Core Banks at Cape Lookout Na- eo monitoring should entail measuring dis-
tional Seashore and Hatteras Island at Cape tances to sources of disturbance. Recording
Hatteras National Seashore (McGowan 2004). nests for longer periods of time also would
The negative association between percent alleviate a great deal of uncertainty. Sabine et
time incubating and daily nest survival seems al. (2005) were very successful in studying
counterintuitive. Conway and Martin (2000) nest success of oystercatchers in Georgia by
showed that birds balance the costs ofegg ex- using time-lapse videography throughout the
posure with those of high parental activity. incubation period.
Birds with high levels of nest-predation pres- Our simplified approach of categorizing
sure minimize nest-site activity by taking few- nests into low or high levels ofparental activ-
er, longer trips off the nest (Conway and Mar- ity provided a coarse-scale observational mea-
tin 2000). This behavior helps reduce parental sure ofbehavioral responses to recreation and
activity around the nest, but it also reduces the disturbance; we expected this to reduce ob-
amount of incubation. American Oystercatch- servation errors. Other researchers that have
er behavior may reflect a similar trade off; evaluated the effects ofhuman disturbance on
their eggs can tolerate extensive heating and avian behavior used experimental designs
cooling (Nol and Humphrey 1994). In our with defined treatment groups (Robert and
study, several clutches exposed for approxi- Ralph 1975, Tremblay and Ellison 1979, Ver-
492 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 118, No. 4, December2006
hulst et al. 2001, Stolen 2003). We studied the perature and nest depredation. Evolution 54:670-
effects of ambient human disturbance caused 685.
by park staff and recreational visitors to de- Davis, M. B. 1999. Reproductive success, status and
viability ofAmerican Oystercatcher Haematopus
tneesrtmiinnge swuhcecteshse.rFiuttwuraes sltiundkieeds toofphautmtearnnsaoc-f pvaelrsliitayt,usR)a.lMe.iSghc.. thesis, NorthCaroli(naStateUni-
tivity and oystercatcher nesting success that Davis, M. B., T. R. Simons, M. J. Groom, J. L. Weav-
compare the behavior of birds on beaches er, and J. R. Cordes. 2001. The breeding status
closed to vehicle and pedestrian traffic with ofthe American Oystercatcher on the East Coast
the behavior of birds exposed to different of North America and breeding success in North
types and intensities of human activity are Carolina. Waterbirds 24:195-202.
Fitzpatrick, S. and B. Bouchez. 1998. Effects ofrec-
needed to improve our understanding of the reational disturbance on the foraging behaviours
patterns suggested by this study. of waders on a rocky beach. Bird Study 45:157-
171.
ACKNOWLEDGMENTS Godfrey, P. G. and M. M. Godfrey. 1976. Barrier
island ecology of Cape Lookout National Sea-
We are grateful to J. R. Cordes and M. Lyons for shore and vicinity. North Carolina. U.S. Govern-
their tremendous contributions to this study. We thank ment Printing Office, Washington, D.C.
the National Park Service, the U.S. Fish and Wildlife Hockey, P. A. R. 1987. The influence of coastal uti-
Service, and the U.S. Geological Survey for support- lizationby man on the presumedextinction ofthe
ing this research. WethankM. W. Rikard andthe staff Canarian Black Oystercatcher. Biological Conser-
of Cape Lookout National Seashore, and S. Harrison vation 39:49-62.
and the staff at Cape Hatteras National Seashore, for Hunt, G. L. 1972. Influence of food distribution and
all theirassistance. We thankJ. A. Collazo, K. H. Pol- human disturbance on the reproductive successof
lock, and F. R. Thompson, III, for assistance on the Herring Gulls. Ecology 53:1051-1061.
design and analysis ofthis study, and J. Hostetlerand Jeffery, R. G. 1987. Influence of human disturbance
M. S. Pruett for their assistance with data collection on the nesting success of African Black Oyster-
and management. We thank C. C. McGowan for ed- catchers. South African Journal of Wildlife Re-
iting this manuscript. We are grateful to three anony- search 17:71-72.
mous reviewers for their comments and suggestions Leseberg, A., P. A. R. Hockey, and D. Loewenthal.
for improving this manuscript. 2000. Human disturbance and the chick-rearing
ability of African Black Oystercatcher: a geo-
LITERATURE CITED graphic perspective. Biological Conservation 96:
379-385.
Andres, B. A. and G. A. Falxa. 1995. Black Oyster- Martin, T. E. 1992. Interaction ofnest predation and
catcher Haematopus bachmani). The Birds of food limitation in reproductive strategies. Current
(
North America, no. 155. Ornithology 9:163-197.
Brown, S., C. Hickey, B. Harrington, and R. Gill Martin, T. E„ J. Scott, and C. Menge. 2000. Nest
(Eds.). 2001. The U.S. shorebird conservation predation increases with parental activity: sepa-
plan, 2nd ed. Manomet Center for Conservation rating nest site and parental activity effects. Pro-
Sciences, Manomet, Massachusetts. ceedings of the Royal Society of London, Series
Burger, J. 1981. Theeffectofhumanactivityonbirds B 267:2287-2293.
at a coastal bay. Biological Conservation 21:231- Mawhinney, K. B., B. Allen, andB. Benedict. 1999.
241. Status of the American Oystercatcher (.Haemato-
Burger, J. and M. Gochfeld. 1998. Effects of eco- puspalliatus), on theAtlantic Coast. Northeastern
tourism on bird behaviorat Loxahatchee National Naturalist 6:177-182.
Wildlife Refuge, Florida. Environmental Conser- Mayfield, H. F. 1961. Nestingsuccesscalculatedfrom
vation 25:13-21. exposure. Wilson Bulletin 73:255-261.
Burnham, K. P. and D. R. Anderson. 2002. Model Mayfield, H. F. 1975. Suggestionsforcalculatingnest
selection and multimodel inference: apracticalin- success. Wilson Bulletin 87:456-466.
formation-theoretic approach. Springer-Verlag, McGowan, C. P. 2004. Factors affecting nesting suc-
New York. cess of American Oystercatchers (Haematopus
Carney, K. M. and W. J. Sydeman. 1999. A review palliatus) in North Carolina. M.Sc. thesis, North
of human disturbance effects on nesting colonial Carolina State University, Raleigh.
waterbirds. Waterbirds 22:68-79. McGowan, C. P, T. R. Simons, W. Golder, and J.
Cartar, R. D. and R. D. Montgomerie. 1987. Day- Cordes. 2005. A comparison of American Oys-
to-day variation in nest attentiveness of White- tercatcher reproductive success on barrier beach
rumped Sandpipers. Condor 89:252-260. andriverislandhabitats incoastalNorthCarolina.
Conway, C. and T. Martin. 2000. Evolution ofpas- Waterbirds 28:150-155.
serineincubationbehavior: influenceoffood,tem- National Park Service. 2005. Park visitation report.
McGowan and Simons • HUMAN RECREATION ALTERS INCUBATION BEHAVIOR 493
National Park Service, Public Use Statistics Of- 2005. A simple, inexpensive video setup for the
fice, Denver, Colorado. study of avian nest activity. Journal of Field Or-
Neter, J., M. H. Kunter, C. J. Nachtsheim, and W. nithology 76:293-297.
Wasserman. 1996. Applied linearstatistical mod- Safina, C. and J. Burger. 1983. Effects of human
els, 4th ed. WCB/McGraw-Hill, New York. disturbance on reproductive success in the Black
Nol, E. and R. C. Humphrey. 1994. American Oys- Skimmer. Condor 85:164-171.
tercatcher (Haematopus palliatus). The Birds of SAS Institute, Inc. 2003. SAS, ver.9.1. SAS Institute,
North America, no. 82. Cary, North Carolina.
Norton, D. W. 1972. Incubation schedulesoffourspe- Shaffer, T. L. 2004. A unified approach to analyzing
cies ofCalidridine sandpipers at Barrow, Alaska. nest success. Auk 121:526-540.
Condor 74:164-176. Shaffer,T. L. andF. R. Thompson, III. InPress.Mak-
Novick, J. S. 1996. An analysis ofhuman recreational ing meaningful estimates of nest survival with
impacts on the reproductive success ofAmerican model-based methods. Studies in Avian Biology.
Oystercatchers (Haematopus palliatus): Cape Skutch, A. 1949. Do tropical birds rear as many
Lookout National Seashore, North Carolina. young as they can nourish? Ibis 91:431-455.
M.Sc. thesis, Duke University, Durham, North Stolen, E. D. 2003. The effects ofvehicle passageon
Carolina. foraging behaviorofwadingbirds. Waterbirds26:
Peters, K. A. and D. L. Otis. 2005. Using the risk- 429-436.
disturbance hypothesis to assess the relative ef- Tewksbury, J. J., T. E. Martin, S. J. Hejl, M. J.
fects ofhuman disturbance and predation risk on Kuehn, and J. W. Jenkins. 2002. Parental behav-
foraging American Oystercatchers. Condor 107: iorofacowbird host: caughtbetween the costsof
716-725. egg-removal and nest predation. Proceedings of
Robert, H. C. and C. J. Ralph. 1975. Effects of hu- the Royal Society of London, Series B 269:423-
man disturbance on the breeding success ofgulls. 429.
Condor 77:495-499. Tremblay, J. and L. N. Ellison. 1979. Effects ofhu-
Rodgers, J. A. and S. T. Schwikert. 2003. Buffer man disturbance on breeding of Black-crowned
zone distances to protectforaging and loafingwa- Night Herons. Auk 96:364-369.
terbirds from disturbance by airboats in Florida. Verboven, N., B. J. Ens, and S. Dechesne. 2001. Ef-
Waterbirds 26:437-443. fectofinvestigatordisturbance on nestattendance
Roper, J. J. and R. R. Goldstein. 1997. A test ofthe and egg predation in Eurasian Oystercatchers.
Skutch hypothesis: does activity at nests increase Auk 118:503-508.
nest predation risk? Journal ofAvian Biology 28: Verhulst, S., K. Oosterbeek, and B. J. Ens. 2001.
111-116. Experimental evidence for effects of human dis-
Ruhlen, T. D., S. Abbot, L. E. Stenzel, and G. W. turbance on foraging and parental care in Oyster-
Page. 2003. Evidence that human disturbance re- catchers. Biological Conservation 101:375-380.
duces Snowy Plover chick survival. Journal of Whittacker, D. and R. L. Knight. 1998. Understand-
Field Ornithology 74:300-304. ingwildliferesponsestohumans. WildlifeSociety
Sabine, J. B„ J. M. Meyers, and S. H. Schweitzer. Bulletin 26:312-317.